The present invention relates, in general, to measuring the topography of surfaces, and more particularly, to measuring the topography of a surface by using a combination of atomic force microscopy and scanning tunneling microscopy.
In the past, a variety of techniques have been utilized to determine the topography of a surface, such as the surface of a semiconductor device. Scanning tunneling microscopy and atomic force microscopy represent two imaging techniques used for such purposes. Scanning tunneling microscopy (STM) is a technique of determining a surface's topography by plotting the value of tunneling current that flows between various points on the surface and an STM probe positioned near the surface. The tunneling current's value is inversely proportional to the work function of the material underlying the probe, the higher the work function the lower the tunneling current. Consequently, STM typically is not suitable for surfaces having a variety of materials because the different work functions of the different materials affect the tunneling current thereby causing inaccurate measurements. Additionally, STM cannot be used for insulating surfaces such as silicon dioxide. Since semiconductor devices typically include a layer of silicon dioxide covering a variety of other materials, STM generally cannot be used to accurately determine the topography of a semiconductor device's surface.
Atomic force microscopy (AFM) is a technique commonly utilized to determine the surface topography of materials, including insulating materials. Although AFM is suitable for measuring the topography of conductors and insulators, AFM cannot determine whether a material is a conductor or an insulator. Consequently, AFM cannot accurately delineate between different materials on the surface.
Accordingly, it is desirable to have a method of using a combination of AFM and STM to provide an accurate representation of a surface's topography and material composition, and a method that performs both AFM and STM measurements using the same probe.